A motor that drives a compressor constituting a vehicle-mounted air conditioner is controlled in the operation thereof by an inverter system.
As shown in FIG. 3, a conventional inverter system 1 has hitherto been operating in order to drive a motor 2 at a low voltage obtained by converting a high voltage of not less than 100 V supplied from a high-voltage power source 3 to a voltage on the order of 5 V by use of a noninsulating DC-DC converter 4. This inverter system 1 performs communication via a communication interface 5 to control a vehicle-mounted air conditioner and for other purposes. Other electrical equipment systems of the vehicle including a host ECU 6 and the like for the inverter system 1 operate at voltages supplied from a vehicle-mounted battery power source 7, such as 12 V and 24V. If a high voltage for driving the motor 2 is applied to the other electrical equipment systems for some reasons, this leads to a failure. For this reason, it is ensured that the inverter system 1 and the other electrical equipment systems can perform communication while being insulated by insulating communication connectors 8, such as photocouplers (refer to Patent Document 1, for example).
Patent Document 1: Japanese Patent No. 3351330
In recent years, with the control of vehicles more sophisticated, failure diagnoses and the like of each part of an electrical equipment system of a vehicle have also been carried out. In the conventional inverter system 1, however, a motor-control microcomputer 9 that governs the inverter system 1 cannot be started unless the high-voltage power source 3 side is started up. That is, it is impossible to establish communication between the host ECU 6 and the inverter system 1 at the same time with the application of the vehicle-mounted battery power source 7. Therefore, with the application of the vehicle-mounted battery power source 7 alone, it is impossible to perform a failure diagnosis of a circuit that receives power from the high-voltage power source 3 side.
Therefore, it also conceivable to supply power to the inverter system 1 from the high-voltage power source 3 side in order to perform a failure diagnosis. However, in a case where a switching element 10 for driving the motor 2 or the like is at fault due to a short, since grounding is shared by the motor 2 side and the inverter system 1 side, there is a possibility that both the motor 2 and the inverter system 1 become broken down if a high voltage is applied from the high-voltage power source 3 side to the inverter system 1.
As for an inverter system for a vehicle-mounted air conditioner that controls the operation of a motor for driving a compressor constituting the vehicle-mounted air conditioner, therefore, the present inventors have already presented a technique in that the inverter system for a vehicle-mounted air conditioner comprises a switching element for rotatably driving the motor, a gate circuit for driving a gate of the switching element, a control circuit that controls the supply of a current to the gate circuit, and a communication interface that performs communication with a host control circuit that issues commands to the control circuit from outside the inverter system, and is characterized in that the inverter system for a vehicle-mounted air conditioner is insulated from a first power source that applies a first predetermined voltage to the motor, and receives voltage supply from a second power source that applies a second voltage lower than the first voltage to the host control circuit (Japanese Patent Application No. 2007-55211.
As a result of this, even when shorts and the like have occurred in the circuit to which the first voltage is applied from the first power source, the first voltage is not applied any more to the side of the inverter system for a vehicle-mounted air conditioner and it has become possible to prevent failures in the inverter system for a vehicle-mounted air conditioner.
The present inventors conducted further studies on such an inverter system for a vehicle-mounted air conditioner.
In systems using electricity, it is required to reduce power consumption and standby power requirements even a little and this is not limited to an inverter system for a vehicle-mounted air conditioner. Particularly, in a vehicle-mounted system, reducing standby power requirements during nonuse has become a challenge in order to prevent the consumption of a battery, and also in the inverter system for a vehicle-mounted air conditioner proposed by the present inventors, reducing standby power requirements was demanded.
The present invention has been accomplished on the basis of such a technical challenge, and the object is to provide an inverter system for a vehicle-mounted air conditioner capable of reducing standby power requirements during nonuse.